Responses Of Epichlo? Gansuensis-Achnatherum Inebrians Symbiont To Drought Stress

Achnatherum inebrians(drunken horse grass,DHG)is widely distributed in the native grasslands of northern and northwestern China,and one of the toxic and poisonous grasses to grazing animals.However,it would be conferred strong stress resistances in their natural habitat once it is infected by the Epichlo? endophyte.Endophyte-infected(EI)and endophyte-free(EF)DHGs were employed as sample grasses,in our experiment,to compare their differences of the growth indicators,photosynthetic capacity and nutrient uptake capacity,to explore the regulation mechanism of the endophyte on DHGs growth and physiological functions under drought condition.Our main results showed as follows:1.The field management methods such as watering and sheltering were used to establish moisture(45%-60% relative soil moisture content,RSMC)and drought(≤15% RSMC)soil water content,natural rainfall was regarded as control(20-30% RSMC)soil water content in this filed experiment.Through a two-year experiment,we found that endophyte significantly improved the drought resistance of DHG(P<0.05).The main manifestation was that endophyte significantly increased the chlorophyll content and net photosynthetic rate of DHG under drought stress(P<0.05),with a relative increase of 18.6% and 65.8% respectively,which further significantly increased the plant height,reproductive branch number and biomass accumulation of DHG(P<0.05),with a relative increase of 16.7%,39.6% and 84.5%,respectively.2.A pot experiment involving four different soil water moisture gradients,i.e.extreme drought(15% RSMC),drought(30% RSMC),control(45% RSMC)and moisture condition(60% RSMC),was established in the greenhouse.The EI and EF seeds collected from Xiahe [(Grassland moisture index(K)=2.00] and Yuzhong(K=0.64)were employed,and two different ways of watering were used in this experiment.Our results showed that when the available water mainly concentrated on the soil surface,the endophyte significantly inhibited the growth and development of the DHG seedling root system(P<0.05).There were significant differences at 15% and 30% RSMC(P<0.05),where root biomass of EI seedlings from Xiahe,Yuzhong sites were decreased by 16.5%,11.0% and 20.9%,7.0%,respectively,than the EF seedlings from the corresponding sites.When the available water mainly concentrated in the deep layer of the soil,the endophyte promoted the growth and development of the DHG seedling root system.There were also significant differences at 15% and 30% RSMC(P<0.05),where the root biomass of EI seedlings from Xiahe,Yuzhong sites were increased 14.4%,12.3% and 8.2%,11.9%,respectively,than EF seedlings from the corresponding sites.At 15% and 30% RSMC,the chlorophyll content of EI seedlings from Xiahe,Yuzhong sites was higher than EF seedlings,with a relative increase of 11.3%,12.7% and 9.6%,11.5%.The shoot biomass was also higher than EF seedlings,with a relative increase of 23.7%,14.1% and 8.5%,16.7%.At 60% RSMC,the differences of root system,chlorophyll content,and biomass between EI and EF seedlings from both sites were not significant(P>0.05).Additionally,the drought resistance of DHGs was significantly affected by their maternal habitat type(P<0.05).The seedlings whose parent plant from Yuzhong site had a higher chlorophyll content and shoot biomass than those from Xiahe site,with a relative increase of 3.6% and 10.8%.3.At 15% and 30% RSMC,the endophyte and maternal habitat type significantly affected the content of endogenous hormones,including abscisic acid(ABA),indoleacetic acid(IAA),cytokinin(CtK),as well as N and P content(P<0.05).The ABA and IAA contents of EI seedlings were higher than EF seedlings,with a relative increase of 8.5%,43.4% and 11.7%,11.4% respectively,but CtK content was lower than EF seedlings,with a relative decrease of 13.6%,16.8%.The N and P contents of EI seedlings were higher than EF seedlings,with a relative increase of 20.8%,21.0% and 24.2%,24.3% respectively.The ABA and P contents of the seedlings from Yuzhong site were 20.4% and 113.2% higher respectively,while CtK and N content were 4.1% and 11.5% lower respectively,than those from Xiahe site.4.A ten-week limited water supply experiment showed that there were no significant difference in the water consumption between EI and EF DHG seedlings(P>0.05)during the whole experiment period.However,the net photosynthetic rate and biomass of EI seedlings were significantly higher than those of EF seedlings(P<0.05),with a relative increase of 57.8% and 13.2% respectively.This result indicated that endophyte improved the water use efficiency of DHG seedlings.Additionally,the net photosynthetic rate and dry weight of EI seedlings from Yuzhong site were significantly higher than those from Xiahe site(P<0.05),with a relative increase of 40.8% and 14.7% respectively.While only the difference of net photosynthetic rate between the EF seedlings from two sites was significant(P<0.05),and the net photosynthetic rate of EF seedlings from Yuzhong site was 37.0% higher than those from Xiahe.This result indicated that endophyte may act as a potential material or information carrier in its vertical transmission process,which made the effect of parent plants to offspring on drought resistance be amplified.